feat!: add json() method and remove default object/array coercion

BREAKING CHANGE: object and array schema no longer parse JSON strings by default, nor do they return `null` for invalid casts.

```ts
object().json().cast('{}')
array().json().cast('[]')
```
to mimic the previous behavior

Author: jquense

README.md

@@ -1420,24 +1420,28 @@ The default `cast` behavior for `array` is: [`JSON.parse`](https://developer.moz
 
 Failed casts return: `null`;
 
-#### `array.of(type: Schema): Schema`
+#### `array.of(type: Schema): this`
 
 Specify the schema of array elements. `of()` is optional and when omitted the array schema will
 not validate its contents.
 
-#### `array.length(length: number | Ref, message?: string | function): Schema`
+#### `array.json(): this`
+
+Attempt to parse input string values as JSON using [`JSON.parse`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse).
+
+#### `array.length(length: number | Ref, message?: string | function): this`
 
 Set a specific length requirement for the array. The `${length}` interpolation can be used in the `message` argument.
 
-#### `array.min(limit: number | Ref, message?: string | function): Schema`
+#### `array.min(limit: number | Ref, message?: string | function): this`
 
 Set a minimum length limit for the array. The `${min}` interpolation can be used in the `message` argument.
 
-#### `array.max(limit: number | Ref, message?: string | function): Schema`
+#### `array.max(limit: number | Ref, message?: string | function): this`
 
 Set a maximum length limit for the array. The `${max}` interpolation can be used in the `message` argument.
 
-#### `array.ensure(): Schema`
+#### `array.ensure(): this`
 
 Ensures that the value is an array, by setting the default to `[]` and transforming `null` and `undefined`
 values to an empty array as well. Any non-empty, non-array value will be wrapped in an array.
@@ -1476,9 +1480,7 @@ yup.object({
 });
 ```
 
-The default `cast` behavior for `object` is: [`JSON.parse`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse)
-
-Failed casts return: `null`;
+object schema do not have any default transforms applied.
 
 #### Object schema defaults
 
@@ -1546,6 +1548,10 @@ object({
 });
 ```
 
+#### `object.json(): this`
+
+Attempt to parse input string values as JSON using [`JSON.parse`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse).
+
 #### `object.concat(schemaB: ObjectSchema): ObjectSchema`
 
 Creates a object schema, by applying all settings and fields from `schemaB` to the base, producing a new schema.

src/array.ts

@@ -25,6 +25,7 @@ import {
 } from './util/types';
 import Schema, { SchemaInnerTypeDescription, SchemaSpec } from './schema';
 import { ResolveOptions } from './Condition';
+import parseJson from 'parse-json';
 
 export type RejectorFn = (
   value: any,
@@ -55,24 +56,8 @@ export default class ArraySchema<
       },
     });
 
-    // `undefined` specifically means uninitialized, as opposed to
-    // "no subtype"
+    // `undefined` specifically means uninitialized, as opposed to "no subtype"
     this.innerType = type;
-
-    this.withMutation(() => {
-      this.transform((values, _, ctx) => {
-        if (!ctx.spec.coarce) return values;
-        if (typeof values === 'string') {
-          try {
-            values = JSON.parse(values);
-          } catch (err) {
-            values = null;
-          }
-        }
-
-        return ctx.isType(values) ? values : null;
-      });
-    });
   }
 
   private get _subType() {
@@ -170,6 +155,11 @@ export default class ArraySchema<
     return next;
   }
 
+  /** Parse an input JSON string to an object */
+  json() {
+    return this.transform(parseJson);
+  }
+
   concat<IT, IC, ID, IF extends Flags, IIn extends Maybe<IT[]>>(
     schema: ArraySchema<IT, IC, ID, IF, IIn>,
   ): ArraySchema<

src/object.ts

@@ -29,6 +29,7 @@ import type {
   PartialDeep,
   TypeFromShape,
 } from './util/objectTypes';
+import parseJson from './util/parseJson';
 
 export type { AnyObject };
 
@@ -124,18 +125,6 @@ export default class ObjectSchema<
     });
 
     this.withMutation(() => {
-      this.transform((value, _raw, ctx) => {
-        if (typeof value === 'string') {
-          try {
-            value = JSON.parse(value);
-          } catch (err) {
-            value = null;
-          }
-        }
-        if (ctx.isType(value)) return value;
-        return null;
-      });
-
       if (spec) {
         this.shape(spec as any);
       }
@@ -442,6 +431,11 @@ export default class ObjectSchema<
     });
   }
 
+  /** Parse an input JSON string to an object */
+  json() {
+    return this.transform(parseJson);
+  }
+
   noUnknown(message?: Message): this;
   noUnknown(noAllow: boolean, message?: Message): this;
   noUnknown(noAllow: Message | boolean = true, message = locale.noUnknown) {

src/util/parseJson.ts

@@ -0,0 +1,18 @@
+import type { AnySchema } from '..';
+import type { TransformFunction } from '../types';
+
+const parseJson: TransformFunction<any> = (value, _, ctx: AnySchema<any>) => {
+  if (typeof value !== 'string') {
+    return value;
+  }
+
+  let parsed = value;
+  try {
+    parsed = JSON.parse(value);
+  } catch (err) {
+    /* */
+  }
+  return ctx.isType(parsed) ? parsed : value;
+};
+
+export default parseJson;

test/array.ts

@@ -3,13 +3,13 @@ import { string, number, object, array, StringSchema, AnySchema } from '../src';
 describe('Array types', () => {
   describe('casting', () => {
     it('should parse json strings', () => {
-      expect(array().cast('[2,3,5,6]')).toEqual([2, 3, 5, 6]);
+      expect(array().json().cast('[2,3,5,6]')).toEqual([2, 3, 5, 6]);
     });
 
-    it('should return null for failed casts', () => {
-      expect(array().cast('asfasf', { assert: false })).toBeNull();
+    it('should failed casts return input', () => {
+      expect(array().cast('asfasf', { assert: false })).toEqual('asfasf');
 
-      expect(array().cast(null, { assert: false })).toBeNull();
+      expect(array().cast('{}', { assert: false })).toEqual('{}');
     });
 
     it('should recursively cast fields', () => {

test/object.ts

@@ -36,13 +36,15 @@ describe('Object types', () => {
     });
 
     it('should parse json strings', () => {
-      expect(object({ hello: number() }).cast('{ "hello": "5" }')).toEqual({
+      expect(
+        object({ hello: number() }).json().cast('{ "hello": "5" }'),
+      ).toEqual({
         hello: 5,
       });
     });
 
-    it('should return null for failed casts', () => {
-      expect(object().cast('dfhdfh', { assert: false })).toBeNull();
+    it('should return input for failed casts', () => {
+      expect(object().cast('dfhdfh', { assert: false })).toBe('dfhdfh');
     });
 
     it('should recursively cast fields', () => {